Electricity meter with power supply load management

ABSTRACT

An electricity meter for monitoring electric power consumed from a service line is disclosed. The electricity meter includes a power consumption metering system for measuring the amount of power consumed from the service line, a peripheral device providing a non-critical function, a power converter, and a load management system. The metering system includes a controller and data storage for storing power consumption data. The power converter provides an unregulated voltage output at the terminals of a capacitor for powering the metering system. The load management system selectively couples and decouples the peripheral device from the power converter. The load management system senses the unregulated voltage to determine whether to couple or decouple the peripheral device. A load management system for an electricity meter and a method of managing the loads on the power system of an electricity meter are also disclosed.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.10/661,114, filed Sep. 12, 2003.

FIELD OF THE INVENTION

This invention relates generally to electricity meters and moreparticularly to power supply load management for electricity meters.

BACKGROUND OF THE INVENTION

Electrical utility service providers, or simply utilities, generatepolyphase electrical power, and typically three phase power. Polyphaseelectrical power is alternating current (“AC”) electrical power that issupplied on a plurality of power supply lines wherein the voltagewaveform on each of the power supply lines has a unique phase angle.While only a single phase of the polyphase electrical power maytypically be provided for single family residences, true polyphaseelectrical power is typically provided to larger facilities such ascommercial and industrial facilities.

Utilities monitor energy usage by customers through electricity meters.Electricity meters track among other things, the amount of energyconsumed, typically measured in kilowatt-hours (“kwh”), at eachcustomer's facility. The utility uses the consumption informationprimarily for billing, but also for resource allocation planning andother purposes.

Modern solid state electricity meters typically include microcontrollersand memory for sensing and storing various electrical usage parametersand metrics data. This data is stored in memory and can be referenced byservice technicians and meter readers. Solid state electricity metersalso attempt to store vital billing information, power line events, timestamps, and other metrics in a non-volatile memory once a power lineoutage is detected.

In the past, utility personnel physically observed meter data onmechanical counters or electronic displays. Modem meters still ofteninclude interfaces such as optical ports and displays for on-siteobservation by utility personnel. However, because meters are generallylocated at the facility of the utility customer, such methods of meterreading are labor intensive and expensive. Modem electricity metersattempt to facilitate remote access to meter data by providing optionalcommunications devices.

Thus, many modem electricity meters include electronics modules having ameasurement board and optional electronic assemblies such as on-boardcommunications devices facilitating remote control and programming ofthe meter and remote access to data acquired by the meter. Themeasurement board typically includes the sensors, signal processors,microcontroller and memory for data acquisition and storage, also knownas a metering system or circuitry. The measurement board also typicallyincludes an on-board power supply providing power to the dataacquisition and storage devices and the optional electronic assemblies.

Various types of remote meter reporting systems have been proposedand/or implemented in optional electronic assemblies. Optionalcommunications devices may include relays programmable for KYZ, EOI, LC,DT A, power factor threshold alert and voltage threshold alerts and realtime communications links such as are modems, RS-232, RS-485, radios andpower line transceivers, or the like.

One problem with optional communications devices, and especially withwireless radio communications, in utility meters arises from the highpower requirements of such devices. For example, wireless pagingtechnology can require in excess of one amp of current at approximatelyeight to ten volts. This power requirement far exceeds the powerrequirement for the remainder of the meter circuitry. Typically, evenmore advanced polyphase electric utility meters only requiresubstantially less than one amp of current. As a consequence, if thepower supply in a utility meter is designed to accommodate the worstcase load anticipated due to the presence of wireless pager transmittersor other optional communications devices, the power supply must bedrastically different, and generally much larger, then the power supplyin the same utility meter without such optional communication devices.

The larger capacity power supply both occupies additional space withinthe meter and has increased cost. Because a utility meter is onlyrequired to perform these optional communication functions a very smallfraction of the overall operating time of the meter, such additionalpower generating capacity goes unused for a substantial majority of thetime. As a consequence, the relatively infrequent need for additionalpower does not necessarily justify the additional size, weight and costissues that arise from the use of a large capacity power supply.

Data acquisition and storage hardware and communications hardware areboth typically DC devices. The power supply in electricity metersconverts AC power from the service line to DC power, some of which isstored in storage and smoothing capacitors. As previously stated, boththe data acquisition and storage and optional communications modulesrequire power for operation.

A typical onboard power supply utilized in electricity meters is a widerange switching power supply. A single wide range switching power supplymay supply the power for both the data acquisition hardware and thecommunications hardware. Switching power supplies store DC energy incapacitors. The DC energy stored in the capacitors is typically used tosustain the operation of the microcontroller until the non-volatilememory write cycle is completed (approx. 400 mS) during power outages.The rate at which the DC energy is depleted from such capacitors uponinterruption of the AC power varies significantly when communicationdevices are connected to the main power supply. For example, somecommunications devices could draw up to 250 mA dc during bursts of 100mS and remain idle during several seconds. During start-up, shutdown,heavy load periods or loss of service, the energy stored in thecapacitors can be used by these communications devices before criticaldata is stored resulting in a loss of critical data.

In some electrical devices, load management has been implemented in theperipheral circuitry which incorporated a load control circuit to reducethe peripherals power consumption during line power outages. When loadmanagement is not provided in an electricity meter, excessive capacitiveloads added by external peripherals during the initial startup disturbthe power supply operation e.g. the switcher does not start up becausethe over-current protection is tripped. However, when separate loadcontrol circuitry is provided for each peripheral device, the additionalexpense can be cost prohibitive. Load management seeks to disconnect thecommunications devices when insufficient power is available to guaranteeoperation of data storage functions.

Those skilled in the art will recognize that the primary function of anelectricity meter is to acquire and store data necessary to determinethe electrical consumption. Providing communication for remote dataacquisition and the like is a secondary function of electricity meters.Thus, should the power generated by the on-board power supply beinsufficient to power both the data acquisition and storage hardware andthe communications hardware, whether during start-up, shut-down heavyload periods or power loss, then it is preferable that power be suppliedto the data acquisitions and storage hardware.

Thus, a need exists for a load management system which economicallyfacilitates remote access to the functions of an electricity meter andthe data stored therein while protecting the data from loss duringoutages or overload situations.

SUMMARY

A micro controller based peripheral load management system that engagesand disengages peripheral DC loads from the power supply of anelectricity meter addresses one or more of the above needs, as well asothers.

According to one aspect of the disclosure, an electricity meter formonitoring electric power consumed from a service line includes a powerconsumption metering system for measuring the amount of power consumedfrom the service line, a peripheral device providing a non-criticalfunction, a power converter, and a load management system. The meteringsystem includes a controller and data storage for storing powerconsumption data. The power converter provides an unregulated voltageoutput at the terminals of a capacitor for powering the metering system.The load management system selectively couples and decouples theperipheral device from the power converter. The load management systemsenses the unregulated voltage to determine whether to couple ordecouple the peripheral device.

According to another aspect of the disclosure, a load management systemfor an electrical meter monitoring power usage from a service line isprovided. The meter has a power supply, a data acquisition and storagecircuit and a peripheral device. The acquisition and storage circuitincludes a controller. The power supply is coupled to the service lineand includes a storage capacitor having an unregulated voltage presentacross its terminals. The power supply powers the data acquisition andstorage circuit. The load management system includes a signal generator,an electrically controlled switch having an ON state and an OFF state,and a conductive branch coupled to the peripheral device and includingthe electrically controlled switch. The signal generator generates acontrol signal having a level dependent upon the voltage across theterminals of the capacitor. The state of the switch is dependent uponthe level of the control signal, and when the switch is in its ON statethe peripheral device is electrically coupled to and powered by thepower supply when the switch is in its OFF state the peripheral deviceis electrically decoupled from the power supply.

According to another aspect of the disclosure, a method of managing theload on a power supply in an electricity meter having a power supplyconverting service line power to regulated dc power using circuitryincluding a storage capacitor having an unregulated voltage across itsterminals, metering circuits coupled to the power supply output andutilizing a controller to acquire data and memory to store data and aplurality of peripheral circuits each configured to be selectivelycoupled to the power supply output when mounted within the meter isdisclosed. The load management method includes the steps of sensing thepresence of the unregulated voltage, selecting one of the plurality ofperipheral devices and mounting the selected peripheral device in themeter and using the controller to compare the sensed unregulated voltageto a threshold value to decide whether to couple or decouple theselected peripheral device and the power supply. The selected peripheraldevice is coupled to, or decoupling from, the power supply based on theoutcome of the deciding step. The comparing, deciding and coupling ordecoupling steps are then repeated.

Additional features and advantages of the present invention will becomeapparent to those skilled in the art upon consideration of the followingdetailed description of preferred embodiments exemplifying the best modeof carrying out the invention as presently perceived.

BRIEF DESCRIDTION OF THE DRAWINGS

The illustrative device will be described hereinafter with reference tothe attached drawings which are given as non-limiting examples only, inwhich:

FIG. 1 is an exploded view of an electricity meter showing a printedcircuit board containing a power supply, data acquisition and storagehardware and a load management system and an optional printed circuitboard containing communications hardware;

FIG. 2 is a block diagram of the power supply, data acquisition andstorage hardware, optional communications hardware and a firstembodiment of a load management system;

FIG. 3 is a schematic block diagram of the data and acquisitionhardware, communications hardware and load management system for a powersupply including a full wave bridge, a switcher controller with overcurrent protection, a transformer, a diode and storage capacitor and avoltage regulator;

FIG. 4 is a schematic diagram of a load management system implementationof FIG. 3;

FIG. 5 is a flow diagram of a load management algorithm implemented bythe load management systems disclosed herein;

FIG. 6 is a block diagram of a second implementation of an electricitymeter with load management control; and

FIG. 7 is a schematic block diagram of the electricity meter with loadmanagement control of FIG. 6.

DETAILED DESCRIPTION OF THE DRAWINGS

As shown for example, in FIG. 1, electricity meters 10 include coils 12having blades 14 passing through a base plate 16 for coupling to theelectrical service line 50 (see FIGS. 2 and 3) from which powerconsumption will be monitored. A PWB, register or measurement board 18is provided on which hardware is present for acquisition, processing andstorage of power consumption data and other metrics. Such hardware isreferred to herein as data acquisition and storage hardware 30. Dataacquisition and storage hardware 30 (see FIG. 2) implements the primarycritical function of the electricity meter 10, i.e. to acquire and storepower consumption data for access by utility personnel.

As shown for example, in FIG. 1, the electricity meter 10 includes aninterface illustratively including an optical port 20 and a display 22for, among other things, optically displaying acquired data for on-siteobservation by utility personnel. Optional printed circuit boards 24 areoften included in electrical meters 10 to expand the user interfaces byproviding additional communication options for downloading andtransmission of acquired data. Among the typical communication optionsare modems, RS-232, RS-485, radios, power line transceivers and relays.The hardware for implementing each of these communications options, andother hardware for implementing non-critical functions of electricitymeters, will be identified herein as optional communication devices orperipheral devices 31. Such optional communication devices or peripheraldevices 31 are represented schematically in FIG. 3 by a capacitive load78 and a resistive load 86.

The data acquisition and storage hardware of measurement circuit 30 mayinclude one or more processors and associated circuitry. Suchmeasurement and control circuits for use in utility meters 10 are wellknown. In many cases, the measurement circuit 30 involves a combinationof a digital signal processor and a microprocessor or microcontroller.Examples of such a circuit include the combination of the conversioncircuit and micro controller in U.S. Pat. No. 6,112,158, to Bond, etal., the front end CPU 44 and register CPU 50 of U.S. Pat. No. 5,471,137to Briese et al., and the AID and DSP 14 and micro controller 16 of U.S.Pat. No. 5,544,089 to Hemminger et al., all of which are incorporatedherein by reference.

The measurement circuit 30 is preferably coupled to a display 22 that isoperable to display metering information. The structure and operation ofsuch displays would be known to those of ordinary skill in the art.

The primary power supply 28 is a circuit that obtains primary electricalpower from a primary power source 50 and generates primary bias powerfor the meter 10. In the embodiments described herein, the primary powersupply 28 may suitably be connected to power line <1>c to obtain primaryelectrical power therefrom. The primary power supply 28 provides theprimary bias power to one or more digital circuits within the meter 10,such as, for example, the measurement circuit 30 and the display 22. Theprimary power supply 28 furthermore provides primary bias power tocircuits in peripheral device 31.

In a preferred embodiment, the primary power supply 28 is a switchedmode power supply, which is well known in the art. The primary powersupply 28 is preferably designed to have a maximum current output ofapproximately 200-300 milliamps. Switched mode power supplies havingsuch capabilities are well known in the art.

Advanced electricity meter 10 acquires and stores in memory 32 variousdata related to power consumption and other metrics. The term metric(kM) refers to any electrical units being measured. Typical metrics arewatthours, VA hours, kV A, kV AR, volts, and amps. Other values such aspower factor are based upon these measurements. Advanced electricitymeter 10 includes a microcontroller 36 and/or microprocessors todetermine these other values from the metrics.

The disclosed electricity meter 10 also provides various communicationsfunctions to permit uploading new programming for onboard controller 36and microprocessors, and for accessing or downloading stored data. Someof these communications functions are provided by a display 22 that canbe operated by a meter reader or technician. Other information must beacquired using different communication interfaces. The disclosed meter10 includes a standard optical interface 20 permitting meter readingonsite by a meter reader using any DGCOM device.

An ANSI Type II optical communications port 20 is mounted on the meter10 and is accessible through the meter cover 26. The optical port 20provides bi-directional communications between the data acquisition andstorage hardware 30 present on the register board 18 and an externalprogrammer or reader. All locations in the memory 32 are readable viathe optical port 20. Communications through the optical port 20 is at9600 baud and is asynchronous. Data transfer is compatible with a PCserial port. The illustrated optical port 20 utilizes an LED that isillustratively shared by a calibration output. Whenever the meter 10 isnot communicating through the optical port 20 with a DGCOM device, theLED will pulse at a rate proportional to the watt-hours flowing throughthe meter 10. Other programmed metrics may be tested by manuallyscrolling to the appropriate metric calibration pulse display causingthe LED to pulse proportional to that metric.

While shown in FIG. 1 as a single printed circuit board, optional PCB 24is representative of a plurality of printed circuit boards implementingvarious communications options. Optional communications devices 31present on optional PCB 24 may include relays programmable for KYZ, EOI,LC, DT A, power factor threshold alert and voltage threshold alerts orreal time communications links such as modems, RS-232, RS-485, radiosand power line transceivers, or the like.

For example, an optional board 24 for MODEM communications provides analternate communication channel to the meter 10. The basic operation ofthe MODEM is to allow access to the meter 10 from a typical telephoneconnection. Once a telephone connection is established, all functionsthat are normally available through the optical port 20 are availablethrough the MODEM.

An optional board 24 for RS-232 communications provides anotheralternate communications channel to the meter 10. RS-232 communicationsare transmitted via an isolated three-wire interface located in themeter's base 16 using an RJ-11 connector. The three lines (transmit,receive, and ground) each provide 2500 V_(rms) isolation. This interfaceuses the same DGCOM protocol as the optical port 20.

In the illustrated meter, the optional communications boards 24 areinstalled parallel to register board 18. Both register board 18 andoptional communications boards 24 include 12-pin headers facilitatingcoupling of the two using ribbon connectors. In the case where a relayboard is also present, optional communications boards 24 may be daisychained by plugging into a 12-pin header on optional relay board 24.

The peripheral device 31 present on optional PCB 24 typically drawspower from the same on-board power supply 28 that powers the dataacquisition and storage hardware 30. In the illustrated embodiment,optional communications board 24 includes power conditioning circuitry,not shown, thereon for regulating an unregulated voltage output by themeter's power supply 28. As mentioned above, optional communicationsdevices 31 often require power to be provided at different voltage andcurrent levels than required by data acquisition and storage hardware30.

The disclosed load management system 40 provides controlledstart-up/power-down operation of the power supply 28 under a widevariety of loading scenarios. By using a low cost solid state switch 58controlled by a signal generated in the controller 36 already utilizedin electricity meter 10, a lower cost solid state electricity meter 10is provided that can accommodate optional communications devices 31while securing acquired data against loss during power outages.

The illustrated solid-state electricity meter 10 stores vital billinginformation, power line events, time stamps, etc. in a non-volatilememory 32 once a power line outage is detected. The DC energy stored inthe capacitor 34 present in the power supply 28 sustains the operationof the microcontroller 36 and the non-volatile memory 32 until the writecycle to the non-volatile memory 32 is completed. In the illustratednon-volatile memory, the write cycle takes approximately 400 mS.

The rate at which the DC energy stored in the storage capacitor 34 ofthe power supply 28 is depleted varies significantly when optionalcommunication devices 31 are connected to main power supply 28. Asmentioned above, some peripheral devices 31, such as radios or wirelesspagers, are capable of drawing up to 250 mA dc during bursts of 100 mSand remain idle during several seconds. In the event of a power outage,if such peripheral devices 31 are not disengaged from the power supply28, the energy stored in capacitor 34 may be depleted before thecompletion of a write cycle resulting in loss of power consumption data.Additionally, under the diverse loading conditions experienced whenperipheral devices 31 are coupled to power supply, the charge oncapacitor 34 can be depleted even without a power line outage.

Previously power supplies in electricity meters with optionalcommunications devices were often designed to handle the worst case loadconditions. However, worst case load conditions rarely occur duringoperation of an electricity meter equipped with optional communicationsdevices 31. Thus, during the large majority of the time that theelectricity meter 10 is in operation, such a worst case power supplydesign is more robust than required. As previously stated, additionalrobustness results in additional costs. The disclosed microcontrollerbased peripheral load management system 40 engages and disengages theperipheral devices 31 from the power supply 28. Such load managementfacilitates optimization of the design of the power supply 28 in theelectricity meter 10. The disclosed load management system 40facilitates designing a power supply 28 with a significant costadvantage over the traditional worst case power supply design.

Illustratively, the power supply 28 is provided on the measurement board18 to power the data acquisition and storage circuits 30 on themeasurement board 18 and any peripheral devices 31 on the optionalboards 24. Illustratively, the power supply 28 is a wide range switchingpower supply that couples to the line voltage 50. Switching powersupplies 28 with a wide operating range (96V_(rms) to 556 V_(rms)) arewidely used in the design of industrial solid-state electricity meters10. As shown, for example, in FIG. 3, the illustrated switching powersupply 28 includes a transformer 42, a rectifier 44, a switchercontroller 46 and a capacitor 34.

The illustrated rectifier 44 is a full wave bridge rectifier thatinverts the negative portion of the line signal 50. Switcher controller46 limits the amplitude of the rectified signal by pulsing on and off tolimit the amplitude of the rectified signal. This rectified amplitudelimited line signal then passes through the primary coil of transformer42. If the current present in the primary coil of transformer 42 becomesexcessive, switcher controller 46 includes overcurrent protection 76that acts to reduce the current in the primary coil. A scaled rectifiedamplitude limited signal is present on the secondary coil of transformer42. The storage capacitor 34 coupled across the terminals of thesecondary coil of the transformer 42 is charged by the scaled rectifiedamplitude limited voltage signal to provide an unregulated voltageV_(UR) across the terminals of the capacitor 34. The unregulated voltageis regulated by a voltage regulator 48 which provides a regulated DCsignal for powering the data acquisition and storage hardware 30 on themetering board 18. The unregulated voltage is also coupled through aswitch 58 to whatever peripheral devices 31 that may be present onoption boards 24.

In a variety of situations, including, but not limited to, operating atlow line voltages and fully loaded during start-up or during a powerline outage, the switching power supply 28 may not supply sufficientpower for operation of both the data acquisition and storage hardware 30and the peripheral devices 31. The disclosed load management system 40disengages the peripheral devices 31 from the power supply 28 until thepower supply 28 is in full regulation or when it is sensed that thepower supply 28 is no longer fully regulated. The illustratedintelligent load management system 40 for electricity meter 10 is basedon a microcontroller 36 that engages and disengages peripheral devices31, and the capacitive loads 78 and resistive loads 86 associatedtherewith, from the power supply 28 under certain specified conditions.

The disclosed load management system 40 disengages peripheral devices 31when either one of two conditions are met. If the actual energy storedin the storage capacitor 34 of the main power supply 28 is below athreshold voltage, the illustrated load management system opens switch58 to disengage the peripheral device 31 present on the option board 24.Also, upon the initiation of a start-up or power-down sequence, theillustrated load management system opens switch 58 to disengagedperipheral devices 31 present on the option board 24.

Illustratively, switching power supply 28 includes an intermediateoutput of an unregulated voltage V_(UR) 52 and a regulated voltageoutput 54. Illustratively, the regulated voltage output 54 by switchingpower supply 28 is +5 V dc. Regulated voltage 54 is provided to powerthe integrated circuits including sensors 56, memory or registers 32 andmicrocontroller 36 and other components present on the data acquisitionand storage hardware 30 on the register board 18. Peripheral devices 31powered by the switching power supply 28, such as modems, KYZ options,RS-232/RS-485, radios, etc., that may pose a heavy loading on switchingpower supply 28 are disabled during the initial start-up period. Onceswitching power supply 28 has reached its steady state operation, loadmanagement system 40 enables the operation of the peripheral devices 31.Furthermore, during the loss of AC power, load management system 40disengages all peripheral devices 31 early in the power down sequence toallow more time to store service related information in non-volatilememory (EEPROM) 32.

As shown for example in FIGS. 3 and 4, the load management system 40includes an electrically controlled switch 58 having an ON state whereinpower is supplied to the peripheral devices 31 and an OFF state whereinpower is not supplied to the peripheral devices 31. The disclosed loadmanagement system 40 implements electrically controlled switch 58 usinga transistor 62 and resistors 64, 66. In the disclosed embodiment ofload management system, the transistor 62 is a high current PNPtransistor for switching applications available from ON Semiconductor,5005 East McDowell Rd., Phoenix, Ariz. 85008 as part No. MMBT6589T1.Other transistors, relays, and switches may be used within the scope ofthe disclosure.

Illustratively, a voltage divider includes a first resistor 64 and asecond resistor 66. Illustratively, first resistor 64 is a 10 kOhmresistor and second resistor 66 is a 1 KOhm resistor. These resistorvalues are selected to provide a gate voltage sufficient to turntransistor 62 fully on when the LOAD_CONTROL signal is present on theappropriate pin of microcontroller 36.

Illustratively, switch 58 is responsive to a LOAD_CONTROL signal 60generated under conditions described below. Illustratively, theLOAD_CONTROL signal 60 is generated by the microcontroller 36. Meter 10includes the microcontroller 36 for digital signal processing of, andfor calculation of power consumption data from, metrics sensed bysensors 56. The illustrated embodiment of the load management system 40utilizes the microcontroller 36 already present on the register board 18to implement a signal generator 68 (see FIG. 2) of the load managementsystem 40. Illustratively, LOAD_CONTROL signal 60 is generated by themicrocontroller 36 that is an 8-bit microcontroller available from NECas part No. uPD78F0338.

In the illustrated meter 10, the microcontroller 36 is already presenton the register board 18 and is programmed to generate an alert signalwhen voltage is low on R_ATTN line. This signal is illustratively usedalso as LOAD_CONTROL signal 60. It is within the scope of thedisclosure, for LOAD_CONTROL signal 60 to be generated by other signalgenerators 68 such as controllers, processors, logic circuits and thelike.

In the illustrated embodiment, the microcontroller 36 sensescontinuously the unregulated output (V_(UR)) of the auto-rangingswitching power supply 28 through one of its analog inputs (analog todigital converter input PI0/ANI0, pin#27). The unregulated output of thecapacitor 34 may be too high at times for input directly into themicrocontroller 36. Therefore, the unregulated voltage (V_(UR)) isconditioned with a voltage divider 70 including a first conditioningvoltage divider resistor R_(C2) 72 and a second conditioning voltagedivider resistor Rc2 74. Illustratively, the first conditioning resistor72 is a 24 Kohm, 1/16 Watt, 1% tolerance resistor and the secondconditioning resistor 74 is a 10 Kohm, 1/16 Watt, 1% resistor.

The illustrated switching power supply controller 46 possesses aninternal over-current protection 76 that shuts down the switching powersupply 28 when the current flowing through the primary of thetransformer 42 exceeds a reset threshold. As soon as the current returnsto safe levels, the switching power supply 28 is enabled by the switchercontroller 46. An appropriate switcher controller 46 may be selectedfrom the TinySwitch Family, available from Power Integrations, Inc.,5245 Hellyer Avenue, San Jose, Calif. 95138 USA. The illustratedswitcher controller 46 is part No. TNY253 from that family of switches.It is within the scope of the disclosure for other switching controllersto be used in the power supply 28.

Typically during the initial start-up process, the switching powersupply) 28 has to charge all the capacitive loading connected to thesecondary side of the transformer 42. In the illustrated embodiment,this includes storage capacitor 34 of power supply 28 and the capacitiveload 78 of the option peripheral device 31. Additional capacitive loadsmay be present on the main board 18 such as the optional mass memorystorage (“RAM”) 25, as shown, for example, in FIG. 1. These sometimesheavy loads create peak currents in the primary side of transformer 42that trigger the over-current protection 76 of the switcher controller46 forcing the power supply 28 to shut down. This phenomenon iscompounded in a wide range switching power supply 28 when it has tostart up at the low end of its operating range fully loaded. Thedisclosed load management system 40 is removes the capacitive load 78and resistive load 86 associated with the optional peripheral device 31during the critical start-up/power-down cycles. Peripheral devices 31are then engaged to main power supply 28 under certain conditionsexplained below.

As shown for example in step 510 in FIG. 5, load management system 40initially determines whether meter 10 is in start-up mode. If so, loadmanagement system 40 determines in step 512 whether peripheral devices31 are disengaged. If the peripheral devices 31 should be disengaged butare not disengaged, load management system 40 disengages the peripheraldevices in step 514. Once the peripheral devices are appropriatelydisengaged, load management system 40 keeps the peripheral devicesdisengaged until it determines in step 516 that the unregulated voltageV_(UR) exceeds a first threshold voltage V_(TH1). Once the regulatedvoltage exceeds the first threshold voltage, the start-up sequence iscomplete and load management system 40 then determines in step 518 if apower-down sequence has started.

Once it is determined that meter 10 is not in start-up mode, or afterdisengaging the peripheral devices 31 because meter is in start-up modeand waiting until the unregulated voltage has reached the firstthreshold voltage, the microcontroller 36 determines whether meter isgoing through a power-down mode in steps 518 and 520.

Illustratively two methods are used to determine if a meter 10 is goingthrough a power-down mode. If the power-down mode is user implemented,then microcontroller 36 detects the presence of a user implementedsignal initiating a power-down in step 518. If the meter 10 is goingthrough a user implemented power down mode, load management system 40determines in step 512 whether peripheral devices 31 are disengaged. Ifthe peripheral devices 31 should be disengaged but are not disengaged,load management system 40 disengages the peripheral devices in step 514.The peripheral devices remain disengaged until it is determined in step516 that the unregulated voltage has again exceeded the first thresholdvoltage.

If the user has not initiated a power down sequence, but the unregulatedvoltage is determined in step 520 to be less than or equal to a secondthreshold voltage then the load management circuit 40 in steps 512 and514 disengages the peripheral devices 31 if they are not alreadydisengaged. The peripheral devices remain disengaged until it isdetermined in step 516 that the unregulated voltage has again exceededthe first threshold voltage. A non-user implemented power-down sequencemay result from, among other things, a power line outage or excessiveloads on the power supply 28.

If there is no uncompleted start-up or power-down cycle in progress,then load management system 40 determines in step 522 whether theperipheral devices are engaged to the power supply. If the peripheraldevices 31 are not engaged but they should be, then in step 524 the loadmanagement system 40 engages the peripheral devices 31. Once theperipheral devices are connected to the power supply 28 the loadmanagement system 40 continues to check for the presence of a power-downsequence by repeating steps 518, 520, 522.

Thus, as shown, for example, in FIG. 5, based on the sampled unregulatedvoltage (V_(UR)), the micro controller 36 engages in a load managementdecision making process. The microcontroller 36 determines through itsPIO/AN10 input if the peripheral device 31 should be decoupled from theswitching power supply 28 by comparing the sensed unregulated voltage toa threshold voltage. The first and second threshold voltages V_(TH1) andV_(TH2) are selected to ensure that peripheral devices are connected tothe power supply 28 only when power supply 28 is within its steady stateof operation. In the illustrated example, the micro controller 36determines if V_(UR)=12V_(dc)+_(—)10% or if the meter 10 is goingthrough a start-up or a power-down cycle. During the initial start-upcycle, the microcontroller 36 disengages the capacitive load 78 andresistive load 86 associated with peripheral devices 31 by switching thetransistor 62 to its OFF state to allow the switching power supply 28 toreach its steady state operation. The transistor 62 is switched to itsOFF state by presenting a digital low signal at the base 80 of thetransistor 62 prohibiting current flow from the emitter 82 to thecollector 84. In the illustrated load management system 40, the digitallow signal is generated by the microcontroller 36 and is present on itscontrol line P40 which is coupled to the base 80 of the transistor 62.Once V_(UR) reaches steady state, the microcontroller 36 turns thetransistor 62 to its ON state by presenting a digital high LOAD_CONTROLsignal 60 on control line P40 coupled to the base 80 of the transistor62 allowing current flow between the emitter 82 and the collector 84thereby connecting peripheral devices 31 to power supply 28.

Similarly, if the external capacitive loads 78 imposed by the peripheraldevices 31 such as radios, pagers, etc cause the switcher controller 46to trigger its over current protection 76, the microcontroller 36 sensesthat V_(UR) is below its steady state voltage and switches thetransistor 62 to its OFF state. When transistor is in its OFF state, thecapacitive load 78 and the resistive load 86 associated with theperipheral device 31 are disengaged from the power supply 28. OnceV_(UR) reaches steady state, the microcontroller 36 turns the transistor62 to its ON state thereby connecting peripheral device 31 to the powersupply 28. If the addition of the peripheral device 31 causes V_(UR) tofall below its steady state voltage, micro controller 36 again switchestransistor 62 to its OFF state. This cycle may take place several timesuntil the capacitors connected on the load side are fully charged.

In the illustrated embodiment of the load management system 40, themicrocontroller 36 senses the energy stored in the power supply storagecapacitor 34 and determines whether meter 10 is experiencing a linepower outage. Based on this information, it engages or disengagesperipheral device 31 by closing or opening the solid state switch 58that controls the power delivered to the peripheral device 31. Thus, inthe disclosed embodiment of load management system 40, the decision toengage or disengage the peripheral device 31 is made in a centralizedlocation. In the event that a plurality of peripheral devices 31 arepresent in meter 10, once the decision to engage or disengage is made,all peripheral devices 31 are engaged or disengaged. Thus the loadmanagement function is centralized.

Illustratively this centralized determination or load managementdecision is made by the microcontroller 36 already present on PWB board18. Additionally, load management system 40 includes a singlecentralized electrically controlled switch that simultaneously engagesand disengages all optional peripheral loads 24. By transferring theload management functionality from the optional peripherals 24 to thecentral microcontroller 36 in the electricity meter 10, the in rush ofcurrents that could cause false start-up cycles in the switching powersupply 28 under heavy capacitive loads is reduced. Thus, a less robustpower supply 28 is utilized in the disclosed meter 10 providing optionalcommunications devices 31. The disclosed load management system 40facilitates power supply design optimization since the power supply 28need not be robust enough to power both critical and non-criticaldevices until the micro controller 36 enables the switch 58.Additionally, the overall cost of a series of meters 10 with optionalfeatures 31 can be significantly reduced as option boards 24 need not beimplemented with load management hardware thereon.

An alternative embodiment of a load management system 140 is shown forexample in FIGS. 6-7. Alternative load management system 140 can beutilized with peripheral devices 131 present on option boards 124 thatinclude switches 158 for selectively disconnecting and connecting thecircuitry of the peripheral device 131 in response to a signal. Likeload management system 40, load management system 140 facilitatescentralized load management decision-making. Thus, while each optionalboard 124 upon which a peripheral device 131 is present must include itsown electrically controlled switch 158, it need not include logiccircuitry capable of making load management decisions. The switches 158are relatively inexpensive when compared to the sensors and logiccircuits required to sense voltage levels and implement decisions basedupon the sensed voltage levels. Also, similar power supply designoptimization can be achieved using the second embodiment of the loadmanagement system 140 as can be achieved using the first embodiment ofthe load management system 40. Thus, much of the cost savings realizedby using load management system 40 can also be realized using loadmanagement system 140 in electricity meters 10, 110.

FIG. 6 shows a linear power supply 128 in a single-phase solidstate-electricity meter 110. DC power is provided by the power supply128 to the data acquisition and storage hardware 130 and thenon-volatile memory 132 under any operating condition until the energystored in the storage capacitor 134 in power supply 128 is notsufficient to sustain their continuous operation. Optional peripheraldevices 131, illustratively optional communications devices such asradios, power line carrier transceivers, radios, etc, are selectivelyengaged or disengaged from the power supply 128 in response to aLOAD_CONTROL signal 160 generated by the microcontroller 136. Themicrocontroller 136 selects the value of LOAD_CONTROL signal 160 basedon the DC energy available at any particular time. The availability ofDC energy is determined by sensing the unregulated voltage V_(UR) acrossthe terminals of storage capacitor 134 in power supply 128.

Operation of load management system 140 is substantially similar tooperation of load management system 40. The algorithm illustrated inFIG. 5 may be implemented in either load management system 40 or 140.During a start-up cycle, all peripheral devices 131 are disengaged bythe microcontroller 136 sending a logical low LOAD_CONTROL signal 160 toall of the switches 158 on option boards 124. The microcontroller 136continues to send a logical low LOAD_CONTROL signal 160 until theunregulated voltage V_(UR) across the storage capacitor 134 reaches afirst threshold value (V_(TH1)). Once the unregulated voltage is greaterthan the first threshold voltage (V_(UR)>V_(TH1)), the operation ofperipheral devices 131 is enabled by microcontroller 136 sending alogical high LOAD_CONTROL signal 160 to each option board 124.

During a power down-cycle, either user implemented or as the result of apower outage or excessive load, the microcontroller 136 disengages allperipheral devices 131 when the unregulated voltage is less than orequal to a second threshold voltage (V_(UR)≦V_(TH2)) to guarantee thecompletion of the worst-case 400 mS write cycle of the non-volatilememory 132.

As shown, for example, in FIG. 7, a second embodiment of an electricitymeter 110 with load management control includes a power supply 128, aprinciple load illustratively including data acquisition and storagehardware present on a metering board 118, a peripheral device 131resident on an option board 124 and a load management system 140.Illustratively, power supply 128 taps AC lines 50 to provide power tothe power supply 128. A transformer 142 steps down the voltage from theline 50 and supplies the stepped down voltage to a bridge rectifier 144.Illustratively, the rectifier 144 is a full wave rectifier. Anappropriate full wave rectifier 144 is available as a single integratedcircuit from Diodes Incorporated, 3050 E. Hillcrest Drive WestlakeVillage, Calif. 91362-3154 as part No. DF02M. It is within the scope ofthe disclosure for rectification to be accomplished using otherintegrated circuits or discreet components. The rectified stepped downvoltage is supplied to a storage/filtering capacitor 134 that acts tosmooth the voltage wave form. Illustratively, the capacitor 134 is analuminum electrolytic 3,300 μF, 25 Vdc low impedance capacitor availablefrom Panasonic USA a division of Matsushita Electric Corporation ofAmerica, as part no. EEUFC1V332.—

In the illustrated meter 110, the unregulated voltage V_(UR), i.e. thesmoothed output of the storage capacitor 134, is present across theterminals of the capacitor 134. The unregulated voltage V_(UR) iscoupled to a voltage divider 152 having a first resistor 172 and asecond resistor 174 providing a conditioned input proportional to theunregulated voltage V_(UR) to the microcontroller 136.

The microcontroller 136 is configured to act in part as a signalgenerator 168 of load management system 140. The signal generator 168generates the LOAD_CONTROL signal 160 regulating the state of theelectrically controlled switch 158 of the load management system 140resident on the option board 124. The unregulated voltage V_(UR) is alsoprovided as an input to the option board 124 and the switch 158. Theunregulated voltage is also provided as an input to a voltage regulator148 resident on the metering board 118. The disclosed voltage regulator148 provides a regulated +5 Vdc signal to the microcontroller 136.

In describing load management systems 40, 140, reference had been madeto microcontrollers 36, 136. In the illustrated electricity meters 10,110, the microcontroller 36, 136 is configured to act as, at least inpart, several systems and implement several functions. Themicrocontroller 36, 136 acts as a signal processor for convertingsignals representative of sensed voltages and currents into values forstorage or further manipulation to generate data for storage. Themicroprocessor 36, 136 acts, at least in part, as a comparator forcomparing the sensed regulated voltage to various threshold voltagevalues. The microcontroller 36, 136 acts to implement the loadmanagement decision function by determining whether a signal should besent to engage or disengage the peripheral devices 31, 131. Themicrocontroller 36, 136 is configured to act in part as a signalgenerator 68, 168 of the load management system 40, 140. While in thedescribed load management systems 40, 140, microcontrollers 36, 136 areused to implement the load management decision and signal generationfunctions of the load management circuits 40, 140, it is within thescope of the disclosure for such functions to be implemented with othercontrollers, processors, integrated circuits, discrete components orcombinations thereof.

As shown, for example, in FIG. 7, the low cost load management system140 includes a signal controlled electronic switch 158 selectivelyproviding unregulated voltage V_(UR) to the peripheral devices 131 whena high LOAD_CONTROL signal 160 is generated by the signal generator 168.Illustratively, signal controlled switch 158 is a discrete low cost PNPtransistor 162 having its emitter 182 coupled to the unregulatedvoltage, its collector coupled to the peripheral device 131 and its base180 coupled through a voltage divider to the unregulated voltage and theLOAD_CONTROL signal 160. Thus, when an appropriate high LOAD_CONTROLsignal 160 is presented at the base 180 of transistor 162, theunregulated voltage V_(UR) passes through the transistor 162 to theperipheral device 131.

As previously stated, the LOAD_CONTROL signal 160 is generated by signalgenerator 168 that in the disclosed embodiment is implemented by themicrocontroller 136 resident of the main board 118. Illustratively, theLOAD_CONTROL signal 160 is presented on the open collector outputalready existing on pin P92 of micro controller 136. Illustratively,transistor 162 is a high current PNP transistor for switchingapplications available from ON Semiconductor, 5005 East McDowell Rd.,Phoenix, Ariz. 85008 as part No. MMBT6589T1. Other transistors, relays,and switches may be used within the scope of the disclosure.Illustratively microcontroller 136 is an eight bit microcontrollerformerly available from Hitachi Semiconductor America, now believed tobe available from Renesas Technology America, Inc., 450 Holger Way, SanJose, Calif. 95134-1368 as part no. HD6473802.

The intelligent load management systems 40, 140 disclosed herein eachmaximizes the energy available for peripheral devices to completecommunications in progress during power fail situations. The loadmanagement systems 40, 140 disclosed herein each also provide adequatereserve energy to complete essential power down storage tasks.Additionally, the load management systems 40, 140 disclosed herein eachfacilitate the design of a lower cost power supply that can sustain theintermittent operation of communication devices.

Although the invention has been described in detail with reference to acertain preferred embodiment, variations and modifications exist withinthe scope and spirit of the present invention as described and definedin the following claims.

1. A method of managing the load on a power supply in an electricitymeter having a power supply operable to convert service line power toregulated dc power using circuitry including a storage capacitor havingan unregulated voltage across its terminals, metering circuits coupledto the power supply output and utilizing a controller to acquire dataand memory to store data, and a plurality of peripheral devices eachconfigured to be selectively coupled to the power supply output whenmounted within the meter, the method comprising the steps of: sensingthe presence of the unregulated voltage; selecting one of the pluralityof peripheral devices and mounting the selected peripheral device in themeter; comparing using the controller the sensed unregulated voltage toa threshold value; deciding using the controller whether to couple theselected peripheral device to, or decouple the selected peripheraldevice from, the power supply based on the outcome of the comparingstep; coupling the selected peripheral device to, or decoupling theselected peripheral device from, the power supply based on the outcomeof the deciding step; and repeating the comparing, deciding and couplingor decoupling steps.
 2. The method of claim 1 further comprising thestep of selecting a second of the plurality of peripheral devices andmounting the second selected peripheral device in the meter wherein thefirst and second peripheral device are coupled or decoupled from thepower supply based on the outcome of the deciding step.
 3. The method ofclaim 1 further comprising the step of providing a switch responsive tothe outcome of the deciding step that is mounted in the meter separatelyfrom any selected peripheral device, said switch being coupled to thepower supply and coupled to the selected peripheral device upon mountingof the selected peripheral device.
 4. A method of managing the load on apower supply line in an electricity meter, the electricity meterincluding at least one peripheral device, the method comprising thesteps of: a) sensing the presence of an unregulated voltage; b)comparing the sensed unregulated voltage to a threshold voltage; c)coupling the at least one peripheral device to the power supply if theunregulated voltage is greater than the threshold voltage; and d)decoupling the peripheral device from the power supply if theunregulated voltage is less than the threshold voltage.
 5. The method ofclaim 4 further comprising the step of repeating steps a) through d). 6.The method of claim 4 wherein the unregulated voltage is sensed across astorage capacitor.
 7. The method of claim 4 wherein the at least oneperipheral device comprises a plurality of peripheral devices.
 8. Themethod of claim 4 wherein the electricity meter further comprises aswitch, wherein the step of coupling the at least one peripheral deviceto the power supply includes placing the switch in an ON state, andwherein the step of decoupling the at least one peripheral device fromthe power supply includes placing the switch in an OFF state.
 9. Themethod of claim 8 wherein the switch is a transistor.
 10. The method ofclaim 4 wherein a controller is used to compare the sensed unregulatedvoltage to the threshold voltage.
 11. The method of claim 4 wherein thethreshold voltage is a second threshold voltage, and further comprisingthe step of comparing the unregulated voltage to a first thresholdvoltage following decoupling of the peripheral device from the powersupply.
 12. The method of claim 11 wherein the unregulated voltage isnot compared to the second threshold voltage again until the unregulatedvoltage is greater than the first threshold voltage.
 13. The method ofclaim 12 wherein first threshold voltage and the second thresholdvoltage are selected to ensure that the at least one peripheral deviceis connected to the power supply only when the power supply is within asteady state of operation.
 14. The method of claim 12 further comprisingthe step of determining whether the electricity meter is in a power downmode if the unregulated voltage exceeds the first threshold voltage.